The efficiency and output power of semiconductor lasers are crucially limited by the heat arising as a result of radiative and non-radiative recombinations of the injected charge carriers.
In order to improve the heat dissipation, optoelectronic components are often provided with a heat sink. In this case, the temperature increase ΔT in the active zone is given by ΔT=Rth·Pv, where Rth is the thermal resistance between the active zone and the heat sink and Pv is the power loss. A temperature increase generally brings about a lower amplification in the case of a semiconductor laser. In order to reduce such a temperature increase which is disadvantageous for the efficiency of the semiconductor laser, it is advantageous to reduce the thermal resistance Rth or the power loss Pv.
By way of example, Kusznetsov et. Al., IEEE Journ. Sel. Topics in Quantum Electronics 5 (3), 561 (1999) discloses improving the thermal linking of the heat sink to the active zone by removal of a substrate that is typically arranged between the active zone and the heat sink. The thermal resistance Rth and the temperature increase ΔT are thereby reduced.
The power loss Pv arising within the active layer is crucially determined by the non-radiative recombination of charge carriers by means of defects or by means of Auger processes, and by radiative recombinations of charge carriers by spontaneous emission. A high recombination rate leads to a short lifetime of the induced charge carriers and thus to a high laser threshold, a low efficiency and output power. It is desirable, therefore, to minimise these types of recombination of charge carriers. The non-radiative recombination of charge carriers by means of defects can be influenced by the quality of the epitaxy. By contrast, the non-radiative recombination of charge carriers by means of Auger processes is difficult to influence.
The spontaneous emission of radiation can be influenced by structures of the order of magnitude of the light wavelength, for example by microresonators or photonic crystals. A detailed presentation of the mode of operation and the methods for production of photonic crystals is contained in the document T. F. Krauss, R. M. De La Rue, Prog. Quant. Electr. 23 (1999) 51-96, the content of which is hereby incorporated by reference.
The influencing of the spontaneous emission by a microresonator is disclosed in the document Y. Hanamaki, H. Akiyama, Y. Shiraki, Semicond. Sci. Technol. 14 (1999) 797-803. U.S. Pat. No. 5,420,880 describes reducing the laser threshold of a surface-emitting semiconductor laser by means of reducing the coupling-out of spontaneously emitted radiation.
Furthermore, WO 98/43329 discloses a vertically emitting laser in which the radiation emitted spontaneously or in stimulated fashion from a first volume region of an active medium in a transverse direction is utilised for pumping a second volume region surrounding the first volume region.